You might try looking under Avisio Options > Sidebar & Footer in the Admin Panel. Find the area called Extra Widget Areas for specific Categories and select the category you want to add a custom widget area. Then hit save and go to Appearance > Widgets and it should be located there.

I think the problem is by default the theme puts some generic widgets in the box if none are specified. The way tofixthis decide which ones you want, find them in the widgets gallery on the right and move them to the footer area. This will give you the options I mentioned. Does that help?